Cassava mosaic disease (CMD) is the
major production constraint on cassava (Manihot esculenta) in Angola.
Previous reports derived from single samples recorded the presence of African
cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV) in Angola. Regional CMD monitoring initiatives have predicted the spread
into northern Angola of EACMV-Uganda (-UG), the unusually virulent recombinant
strain associated with the African CMD pandemic (Legg et al., 2006). In
view of this threat, an assessment survey was conducted in north and central
Angola in April 2008.

Eighteen cassava fields were sampled
in Bengo, Cuanza Norte, Malanje and Uige Provinces. Moderate to severe CMD
symptoms were observed in most fields. Sixty-three of 65 samples obtained from
these fields tested positive in TAS-ELISA using monoclonal antibody SCR 20. PCR
was performed using primer pairs previously described for the specific
identification of ACMV, EACMV, EACMV-UG, East African cassava mosaic Cameroon virus (EACMCV) and Indian cassava mosaic virus (ICMV) (Ogbe et al., 2003), East African cassavamosaic Malawi virus (EACMMV) (Zhou et al., 1998), East African cassava mosaic Zanzibarvirus (EACMZV) (Were et al., 2004) and South
African cassava mosaic virus (SACMV) in mixed infections. This revealed the occurrence of ACMV,
EACMV and EACMV-UG, but not EACMZV, EACMMV, SACMV or ICMV. Single infections of
ACMV and EACMV were detected in 32.3% and 9% of samples, respectively. Mixed
infections of ACMV with EACMV, EACMV with EACMV-UG and all three viruses were
detected in 35.3%, 1.5% and 16.9% of samples, respectively. ACMV, detected in
84.6% of samples, was the predominant species, followed by EACMV (63%) and
EACMV-UG (18.5%). Significantly, EACMV-UG occurred most frequently in the
northernmost part of the surveyed area (Uige Province) immediately to the south
of the Bas Congo region of the Democratic Republic of Congo, already known to be
affected by the pandemic. These findings significantly broaden the known
geographical extent of the CMD pandemic and draw attention to the urgent need
for the large-scale deployment of resistant cassava varieties, which have been
used to reduce losses in pandemic-affected regions of East Africa.

Figure 1: Severe symptoms of EACMV-UG in cassava in a farmer’s field in Uige province, Angola

Figure 2: CMD incidence in various cassava fields surveyed in Angola. Areas of EACMV-UG occurrence are indicated with yellow circles.